The present invention relates to optical lens assemblies for use in lighting devices such as commercial and residential lighting fixtures, flashlights and miniature flashlights and more particularly to optical devices for use with lighting devices of the type employing a high brightness light emitting diode to provide a smooth uniform spotlight beam having sharp edges.
Most commercial lighting devices are designed to provide an on-axis, high intensity peak in their beam distribution as is typically found in flashlights with smooth reflectors. Attempts to provide a more uniform beam distribution include the use of multi-faceted reflectors, however, the resulting beam pattern tends to be Gaussian with no sharp edge between the area illuminated by the beam and the surrounding non-illuminated area. In both the faceted and unfaceted cases, the reflector tends to be parabolic in shape and essentially smears the image taken from the far field of the light source and projects that smeared image in the far field of the flashlight beam.
Other prior art attempts to produce a focused light source include the provision of a standard convex lens with a relatively long convergence factor in front of a Light Emitting Diode (LED) package. These devices also produce an unacceptable result as they capture the far field image from a plane projected in front of the LED package and simply enlarge that image in a reversed pattern in the flashlight beam far field. If the beam pattern is carefully studied, an image of the emitter die and diode reflector cup can be seen in the beam image.
Therefore, there is a need for a lighting device that produces a smooth, evenly distributed beam of light. In addition, there is a need for a lighting device that provides a high intensity beam of light that has a homogeneous illumination pattern. There is also a need for a high intensity flashlight beam that provides a uniform field of illumination and that has a sharp edge between the illuminated field and the non-illuminated field.
In this regard, the present invention provides an improved LED lighting device for producing a high intensity focused light beam that has a uniform appearance across the entire field of illumination and that has a sharp defined edge between the illuminated and non-illuminated areas. The present invention is an improvement over the prior art in that it provides a uniform illumination pattern without producing peak illumination along the axis of the light beam and without creating xe2x80x9chot-spotsxe2x80x9d in the illumination field. In addition, unlike existing products that use parabolic reflectors for focusing the light beam, the uniformity of the pattern of light distribution is not dependant on the distance of the illuminated surface from the flashlight nor does the beam require refocusing as the distance between the light source and the illuminated surface increases.
More specifically, several novel elements are combined to result in the unique appearance of a focused uniform beam of light. The first element is the use of a specialized light emitting diode (LED) component. The LED used in the present invention is customized to provide a concentrated, uniform light output flux across the entire emitter die and reflector cup assembly. This is achieved by providing an LED that has a scatter layer coating, such as a phosphor slurry, covering the reflector cup and emitter die. The uniform scatter layer diffuses the energy emitted from the emitter die thereby causing it to be uniformly distributed over the entire surface of the reflector cup. This scattered light provides a high intensity and uniform light source that is used to generate a smooth and uniform near field light image at a plane located within the LED package between the emitter die and reflector cup assembly and the front of the LED package. The present further invention employs an LED having a clear optical housing with a narrow beam angle that preserves the concentrated near field light image produced by the lighting structure thereby allowing the compact light image to be captured and further focused and imaged into the far field light beam image of the present invention.
FIGS. 4 and 4a, illustrate two types of LED packages available in the prior art. LED packages are produced in both narrow (FIG. 4) and wide (FIG. 4a) beam angles. For purposes of the present invention and as generally understood in the field, the term narrow angle refers to an LED with a beam angle of less than 15xc2x0 and wide angle indicates an LED with a beam angle of greater than 15xc2x0. Generally, the prior art LED packages have an emitter chip 70, a reflector cup 72 and an optical housing 74. As can be seen in the illustrations, the wide angle LED in FIG. 4a provides a greater amount of available luminous flux (illustrated by the ray trace lines) in the LED far field adjacent to the outer optical housing 74 of the LED. While the wide angle LED allows a greater amount of light to be controlled and therefore transmitted by the curved surface of the optical housing 74 thereby producing a greater amount of light, the output pattern and projected image is scattered which results in a very large and unfocused image of the LED package (cup and die) being transmitted to the LED far field. The narrow angle LED shown in FIG. 4, while transmitting less of the total available luminous flux into the far field of the LED, presents a narrower more focused image of the LED package in the LED far field. The present invention employs a narrow angle LED. Although this represents a trade-off in efficiency, in that all of the available luminous flux from the LED is not captured and projected into the far field of the beam, as will be seen later in the description, a high quality focused LED near field image is critical to produce a level beam output.
The other element of the present invention is a unique optical lens that captures an image of the emitter die and reflector cup from the near field plane within the LED package and projects a uniform focused image of the LED near field in the far field of the light beam. This unique lens captures a clear near field image of the reflector cup and emitter die from inside the LED package without interference from the LED optical housing.
The use of the near field image of the LED as the imaging source is considered to be a significant improvement over the prior art. Until now, the prior art has only attempted to utilize the far field image created at a plane beyond the outer surface of the LED optical housing. In contrast, in the in the present invention, the image used to create the far field light image is actually a near field image as taken from a plane within the interior of the LED. This is achieved by the use of a spherical lens placed in close proximity to the LED package such that the convergence point of the lens falls behind the die and reflector cup of the LED. This arrangement captures an image across the entire face of the reflector cup rather that an image of the die alone or a diffuse image of the entire LED package as was the case in the prior art. This technique, referred to as defocusing, allows a uniform image to be obtained by reducing the bright spots and non-uniformities found in a focused image of the LED die alone. Also, this placement of the lens so as to capture an image at a plane along the interior of the LED package further allows the outer edge of the LED reflector cup and/or the circular outer wall of the LED package to act as a field stop to provide a sharp cutoff for the beam image in contrast to a lens placement further from the LED package that images a diffuse light image from the far field distribution of the LED package as a whole.
Accordingly, among the objects of the instant invention is the provision of an illumination assembly that has a focused high intensity beam. Another object of the present invention is the provision of a high intensity lighting assembly that provides a uniformly distributed beam having a far field light image that is uniform in appearance across the illuminated surface. In addition, an object of the present invention is to provide a high intensity light source that produces a focused beam of light having a uniform light distribution across the illuminated field while having a sharply focused and contrasted edge between the illuminated field and the non illuminated field.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.